100%winning Record got bumped down?!?!

[OrangePower]

Originally Posted by jmnk

Well, we just have to disagree here.

Actually, no, you have convinced me, so I recant

Originally Posted by jmnk

In practice, for USTA tennis you can easily normalize via the following:
'the best possible result' is 12 games difference (6:0, 6:0 score) - so that is '1' in ELO calculations
'the worst possible result' is -12 games difference (0:6, 0:6 score) - so that is '0' for ELO calculations.
'the tie' is 0 game difference.

so now if per ELO the expected score for any two players is for example 0.75 than that means that the game difference in that match should be 0.75*24-12=6 (meaning a routine 6:3, 6:3 type of the score)

if the expected score is 0.35 than the game difference (expected) is 0.4*24-12=-3.6. that means that if a lower ranked player lost like 4:6, 6:7 than he actually 'won' since he performed better than was expected.

I think our disagreement centered around the transformation between tennis score and ELO score... your example illustrates your position well. I'm not convinced that such a transformation (or any similar transformation even if non-linear) is valid in terms of the results it produces, but you've convinced me that it could well be the way USTA does it.

Originally Posted by jmnk

yes, thanks for the suggestion. I'm actually painfully familiar with the algorithm, as I have indeed played tournament chess for quite a while.

I've played some in the past myself, so perhaps if we have any further disagreements we can settle them over a combined chess/tennis challenge Then all we need to agree on is how to weigh the results!

[asimple]

I think the key issue here is not the rating system, but the fact that there is an incentive to play at a lower rating for leagues. I took a long period of time off from tennis, and just started to play leagues last year. It is actually a lot of fun, but IMHO it has drastically changed the game. I don't mind the ratings games as much as the new "line is out" philosophy which is common on many teams. The rating system should and probably does do its job assuming its not gamed. In the greater scheme of things there isn't too much difference if a low 4.5 is on a 4.0 team or vice-versa. The real issue is people intentionally gaming the system. Even in this case I don't know that I get it too much. Winning a national 3.5 championship when your a 4.5 player seems pretty lame to me.

My particular case is probably somewhat common. I was a mid 5.0 when I was young, but took many years off and put on 70 pounds. I self rated as a 4.5 last year and had a winning record but got bumped down to 4.0 which was probably a mistake based on the way I was playing. Over the year I decided to get my game back into shape and lost 40 pounds. At this point I am nowhere near a 4.0 and improving. I've played a few matches so far this year, and based on the results I'm pretty sure my rating is nowhere near the 4.0 level anymore. I'm playing both 4.5 and 4.0, but mainly focusing on 4.5, but I guess as lame as it is I too am continuing the 4.0 play.

[schmke]

Originally Posted by asimple

My particular case is probably somewhat common. I was a mid 5.0 when I was young, but took many years off and put on 70 pounds. I self rated as a 4.5 last year and had a winning record but got bumped down to 4.0 which was probably a mistake based on the way I was playing. Over the year I decided to get my game back into shape and lost 40 pounds. At this point I am nowhere near a 4.0 and improving. I've played a few matches so far this year, and based on the results I'm pretty sure my rating is nowhere near the 4.0 level anymore. I'm playing both 4.5 and 4.0, but mainly focusing on 4.5, but I guess as lame as it is I too am continuing the 4.0 play.

This is the challenge for any rating system and especially those like NTRP where there are levels a player plays at. Ignoring any gaming that may go on, player's games may be getting better or worse based on age, practice, physical condition, and so on. So a rating will always be moving one way or another to some degree, for some, that movement may be very significant. The result is that someone may be at the "wrong" level at some point in time during a year until their level is reset at the end of the year.

Your situation sounds like this is occurring "naturally", not through any gaming and this is to be expected, and may result in your 4.0 team having a better chance of doing well. IMHO, this is the natural ebb and flow that results in teams at a given level being better or worse.

But you raised a good point about the incentive for someone to be rated lower than they should be which leads to gaming the system to accomplish that. As long as individuals get a rating and that dictates what level they can play at and teams can be formed more or less from any collection rated at the same level, you are going to have this problem.

One idea (that I have not fully thought through, so just throwing it out for discussion) would be to have a system more like English Soccer (and other similar leagues) where it is a team that is "rated" and plays at a given level and may be promoted up or relegated down based on win/loss performance.

Individuals would still have to have ratings and there would have to be rules about what level team new players can join and to the degree possible these would need to err on the side of having a player on a team at higher level rather than lower, and you'd want to limit roster turnover so a team at a lower level couldn't recruit too many ringers, or force a team to play at a higher level if a roster is a certain percentage new.

Yes, the USTA has the move up or break up rule, but perhaps this needs to be revisited or tightened up.

This may not work with USTA League tennis where teams are less formal than a soccer league, and I'm sure there are other issues, but it is something to think about.

[schmke]

Originally Posted by NumbersGuy

Schmke, when you say "give less weight to matches between mis-matched players, unless there is an upset of course" (italics added), is that really what you meant? Because a tank job looks exactly like an upset to the computer. I think the computer already throws out matches when the players/teams are more than 0.5 apart. I think you touched on a better idea for eliminating tanking, which to eliminate matches that are too far from the "expected range". It would be simple enough for the USTA to do some calculations to identify match results that are outside, say, a 95% frequency of occurrence, and eliminate them from the NTRP calculation on the suspicion of tanking or injury or other unreliable indicator of ability. Yes that would wipe out the occasional wonderful and well-earned upset, but for every one of those I suspect it would also eliminate 20 tank jobs.

Yes, both of the items I mentioned need to be used.

For example, if in a 4.0 match, an about to be bumped to 4.5 (rated very near 4.5) plays a low-end 3.5 that is playing up (rating very near 3.5), he should in theory win 0 & 0. But if he happens to give up a game and wins 1 & 0 an unweighted system would ding the winning player pretty severely. This is a match that should be given less weight because the opponents are far apart.

But you don't want to discredit the match entirely, so if the match does get closer or perhaps even the lower rated player wins, you want to give it more weight. BUT, you also need the "throw a match" check which would look at the "rating profile" of both players and if this match looks like an anomaly, either throw it out or give it less weight.

[jmnk]

Originally Posted by OrangePower

Actually, no, you have convinced me, so I recant

I think our disagreement centered around the transformation between tennis score and ELO score... your example illustrates your position well. I'm not convinced that such a transformation (or any similar transformation even if non-linear) is valid in terms of the results it produces, but you've convinced me that it could well be the way USTA does it.


I've played some in the past myself, so perhaps if we have any further disagreements we can settle them over a combined chess/tennis challenge Then all we need to agree on is how to weigh the results!

hey, i like you already!

back in the days we used to have triathlon of sort: tennis + speed chess + well, 'drinking certain substance that made you play either sport rather challenging' and yes, there were heated discussions on how to combine the score and how to assign weight to each activity. It still brings tears to my eye.

i completely agree that applying ELO to any competition is sort of an art. While it gives you a very well formula to calculate the results you still need to figure out what makes the most sense for input values. For example, i would not be terribly surprised if one found a close correlation between the length of the tennis match and the relative strength of the opponents. So it very well may be that the length should be used as a criteria. like 'if 4.5 plays 4.3 the expected length is 1h45min'. The possibilities are really endless.

Incidentally, since we have touched on doubles vs. singles too. there are other algorithms used in on-line multiplier gaming that supposedly are better than ELO is assessing rankings of the players involved. These concepts are more applicable to doubles in tennis as players may play with different partners, against varying sets of opponents.

glad we could have a nice discussion.

[LuckyR]

Originally Posted by NumbersGuy

For those wondering what the statistical difference is between a 3.68 and a 3.69, see the table below Using a methodology very similar to Schmke's (so I don't have everyone's true NTRPs, just my estimates), and a large database of over 20,000, here's what I calculate. I sure hope the table comes out legibly.

[Rating difference] [% won by higher player]
0.00-0.01 52%
0.01-0.05 55%
0.05-0.10 63%
0.10-0.15 69%
0.15-0.20 72%
0.20-0.25 77%
0.25-0.30 80%
0.30-0.35 83%
0.35-0.40 86%
0.40-0.45 89%
0.45-0.50 91%

I suspect the percentages for the upper categories are somewhat artificially depressed by tanking, but of course have no proof.

So the answer to 3.68 vs. 3.69 is one could expect the 3.69 to win about 52% of the time, based on this admittedly limited sample and imperfect NTRP calculation method.

Wow, that looks like a lot of work (the adding of your estimation of the NTRPs, not the calculation itself).

Of course to get the actual data (perhaps similar or identical to your estimate, or not...) it would not take nearly the effort for the USTA.

A 2% difference by your estimate (using 50% as the standard), seems reasonable at first glance, of course the number is meaningless (or more meaningless, since it is your estimation of the true NTRP) without a mention of the error of the calculation.